Multicarrier signals are predominant in many terrestrial wireless communication systems. There is a growing interest in utilizing multicarrier signals for navigation purposes because multicarrier schemes are effective in combating multipath effects, which are one of the major sources of error for radio frequency (RF) navigation systems due to the bias introduced in the time delay estimate. The time delay estimate (the time difference between when the signal is transmitted and received) is critical to the performance of RF navigation systems since this estimate provides information on the distance between the transmitter and receiver.
Multicarrier systems are sensitive to frequency offsets, which also need to be estimated in order to correctly demodulate the received data. Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation method that has been adopted in standards such as IEEE 802.11a/g, DVB-T/T2, and LTE, so there are numerous signals of opportunity available to use for position estimation, even though these signals were not originally intended for positioning, navigation, and timing applications.
Non-data-aided time and frequency offset estimators have the advantage of not requiring any known training data to estimate some desired parameter, thus preserving high bandwidth efficiency. Non-data-aided estimators can readily adapt to different OFDM standards since they are not reliant on training data which varies across standards. Some non-data-aided approaches jointly estimate the symbol time offset (STO) and carrier frequency offset (CFO) in OFDM systems. However, such methods typically require more than one OFDM symbol to achieve sufficient estimation performance for all signal-to-noise ratios (SNR) due to a flooring effect exhibited at higher SNR. Using multiple symbols is not well-suited for navigation-related applications in which fast acquisition time is critical. Further, methods that use only one complete OFDM symbol exhibit a flooring effect at higher SNR.
A joint time and frequency offset estimator for OFDM systems is needed that utilizes one OFDM symbol and achieves sufficient estimation performance for all SNRs.